Broken spring

Case

A spring of a steam valve was broken after several years of service. Conditions steam 80 bar at 500°C. The lowest winding of the spring, located inside the bonnet at atmospheric conditions, was broken.

Cause

The material of the spring was corroded near the fracture. SEM investigation revealed a typical intergranular fracture surface with pitting at the edges. The morphology is characteristic for hydrogen embrittlement, induced by the cathodic partial reaction of the corrosion process.

Advice

Waterproofing of bonnets and apply insulation to prevent condensation.